Open but not rugged: The awe-inspiring vastness of the Nullarbor

Have you ever experienced “vastness”? Have you driven across a vast expanse of space that stretches from horizon to horizon seemingly without limit? If not, then I can recommend the Australian Nullarbor (pronounced “null-ah-bore”), the treeless arid expanse of red soil and scrubs in between Eucla in Western Australia and Ceduna in South Australia. It surely is one of the world’s vastest expanses of land.

Just don’t run into an emu or a camel. (Yes, they are really out there, together with millions of kangaroos).

But what is vastness, cognitively speaking? What cues induce a perception of vastness? How is the experience of vastness related to other perceptual variables?

Those questions are far from trivial because the effectiveness of most visual cues for visual depth drop off rapidly once the distance exceeds 100 meters (about 300 feet). For example, binocular convergence—that is, the eyes’ tendency to converge towards each as they focus on a single object, which we can detect and exploit as a distance cue—becomes ineffective beyond 2 meters.

So how do we know that we are looking at a vast expanse of space when we are standing in the middle of the Nullarbor and we are looking down the Eyre Highway?

A recent article in the Psychonomic Bulletin & Review took up this question and explored several possible variables. Researchers Roberta Klatzky, William Thompson, Jeanine Stefanucci, Devin Gill, and Kevin McGee focused on two visual variables that structure the shape around a scene, known as openness and ruggedness. Openness refers to the lack of boundary elements—for example, in the opening picture above, there are few (if any) objects that have any boundaries. Ruggedness is related to the number of contours that arise from the ground to obscure the horizon—the above picture obviously does not depict a rugged scene.

In a first experiment, Klatzky and colleagues presented participants with more than 100 full-color pictures of natural environments that ranged from close-ups of vegetation to mountains and beaches. The figure below shows a few examples.

Participants were then given a definition of vastness, namely “a space is vast if it seems to extend without limits away from you, making you feel like a small element within the space”, before being asked to judge each image on how large the depicted space felt. Perhaps not unexpectedly, scenes with a clear horizon line (e.g., an ocean but also mountains) were judged to be the most vast, whereas forests and close views of vegetation were judged to be least vast.

A second experiment addressed the question whether perceived vastness might be the result of the openness and ruggedness variables. That is, how well can vastness be predicted from judgments of openness and ruggedness?

To answer that question, the images from the first experiment were presented to a new group of participants, who had to place each image into a perceptual space formed by the two variables ruggedness and openness. The figure below shows a sample stimulus on the left, and the response grid on the right.

For each stimulus, participants clicked the grid location on the right that most closely matched their perceived conjunction of openness and ruggedness.

Two results from this study were noteworthy. First, there was no linear relationship between ruggedness and openness ratings across the images. The figure below shows the two ratings for all images (each point represents the average rating across participants for a given stimulus on the two dimensions).

Second, and perhaps more important, those ratings from the second experiment could predict the vastness ratings from the first study with considerable accuracy. Specifically, openness alone accounted for 60% of the variance in the first study, and this value increased to 82% when ruggedness was also considered. In other words, knowledge of one group’s openness and ruggedness ratings reduced uncertainty about another group’s perception of vastness by more than 4/5th.

In a final experiment, Klatzky and colleagues examined the role of perceived distance in depth. Participants were asked to judge the distance to the center of the space (for example, the center point between the observer and the horizon in the first figure above) for the same set of images. The instructions were for participants to think of themselves as taking the picture and, from what they would see, “to report the distance from the photographer to the center of the depicted objects and surfaces in the image (not the sky).” Distances could be expressed in any metric (e.g., yards or meters), but for analysis all responses were converted into (perceived) meters.

Two aspects of the results are worth highlighting: First, there was a relationship between judged distance and the vastness ratings from the first study, although that relationship was highly non-linear as shown in the figure below.

Second, when judged distance was entered as another predictor into a statistical model that predicted judged vastness, it was found to reduce uncertainty by a mere 5% after openness and ruggedness had already been considered (and which accounted for more than 80% of the uncertainty in the previous study). One reason for the small size of that effect was the large variability between participants’ estimates: For example the mountain range in the center of the earlier example figure was judged to be 18 miles away on average, but individual estimates ranged from 1 mile to 150 miles away!

In other words, distance matters for size, but the role of distance is far less pronounced than the role of perceived openness and ruggedness.

Klatzky and colleagues provide us with a good first understanding of the variables that create a perception of vastness. The authors suggest that the importance of their results “goes beyond their perceptual implications and the theoretical questions they raise, because vastness appears to be something more than a purely perceptual outcome. An expanded sense of space has been implicated as a precursor to the emotion of awe, which in turn has been linked to well-being, social engagement, and helping behaviors.”